The drugs so far administered to the outer skin have served the purpose of producing a local effect on the outer skin or hypodermal tissues, such as a bactericidal, disinfecting or analgesic effect. However, in recent years, attempts have also been made to administer drugs having a systemic activity to the outer skin, instead of by peroral administration or injection. The percutaneous administration of a drug, particularly a systemic drug, has the following advantages, among others: the drug efficacy can easily be maintained for a long while; the rate of drug absorption can easily be controlled, so that adverse effects due to overdosage can be minimized; since the drug is sparingly metabolized in the liver by the first pass effect as found in the case of oral administration, the drug can be used effectively; and even a drug possibly causing gastrointestinal disorders upon oral administration, such as indomethacin, can be administered safely.
However, the normal skin, which has a body-protecting action, is generally capable of resisting drug absorption or permeation. Therefore, drugs (especially systemic drugs), when simply administered in the conventional forms of ointment, lotion and so on, can scarcely be absorbed into the body in amounts sufficient to produce a satisfactory pharmacological effect.